This invention relates to a vehicular anti skid braking system and particularly to an anti skid braking system for use in pneumatic brakes embodying relay valves.
It is well known that the locking of vehicular wheels during braking action results in a loss of directional control of the vehicle. Various automatic skid control devices have been provided for relieving the brake pressure in response to an incipient skidding condition to prevent or minimize the adverse effects of wheel lockup. Normally these devices include a valve or other structure for isolating the operator applied pressure from the brake actuating mechanism in response to the skid condition. These valves are conventionally rapidly cycled during a given braking operation to successively release and apply the brakes. During the operation of the skid control device, the pressure exerted by the operator on the operator controlled portion of the brake system continues to rise. If this increased pressure is directly transmitted to the brakes on subsequent reapplications during the braking cycle, there is a significantly greater likelihood of wheel lockup during such subsequent applications.
It is, therefore, a principal object of this invention to provide an anti skid braking system that modulates the pressure upon re-applications during a given braking cycle.
It is another object of this invention to provide an anti skid braking system in which the pressure applied to the brakes on subsequent applications during a given braking cycle is reduced to a level that will not promote skidding.
One type of braking system commonly used in tractor trailer type pneumatic brakes embodies a relay valve. Such relay valves have a pilot operated portion that experiences pressure from the operator treadle control and which, in turn, controls the communication between the source of high pressure and the wheel brakes. In connection with this type of braking system, it has been proposed to provide an anti skid by dumping the operator controlled pressure applied to the relay valve to release the brakes and prevent skidding. After the wheels have been permitted to spin up to a certain extent, the brakes are re-applied. If the full treadle pressure is applied to the relay valve the brakes will experience a greater actuating pressure than that which existed at the time the original skidding condition was detected. Thus, on subsequent brake applications the chances of skidding are promoted rather than reduced.
It is, therefore, a further object of this invention to provide an improved skid control system for brakes of the type embodying a relay valve.
It is another object of this invention to provide a relay valve operated skid control system in which subsequent application pressures are modulated to an extent that will not result in skidding.